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A rainbow of no-wrinkle cotton.

A Rainbow of No-Wrinkle Cotton

Rob Reinhardt, Gene Blanchard, and Bob Harper are creating a whole new coloring book - one that will delight the textile industry and fashion-conscious consumers who like the soft touch of cotton but don't like the wrinkles.

These three ARS chemists aren't spending their time with wax crayons. Their medium is a variety of techniques that allow cotton to be dyed after it has been treated with a no-wrinkle finish. The techniques open the door to a broader range of patterns and more vibrant shades for consumers, while also saving industry money. And they don't reduce the breathability, absorbency, and comfort of cotton, says Reinhardt.

Currently, cotton fabrics has to be dyed before a no-wrinkle finish is applied because the chemical bond created by the finishing process repels dyes. "The cotton fiber has to swell to accomodate the molecules of dye," explains Blanchard. "Once the fabric is heated and treated with a no-wrinkle finish, it won't accept those molecules as an untreated fabric would."

This puts the textile and garment industries between a rock and a hard place trying to keep up with the unpredictable and ever-changing fashion world. If textile manufacturers want to produce a wrinkle-free fabric, they first have to dye it and hope the colors will be "in" next season. If garment makers don't want to change being stuck with a large inventory of "out" colors, they buy bleached, untreated fabric that can be dyed in the latest hues before or after the garment is made. As a result, consumers have a limited selection of wrinkle-free cotton garments on store racks.

But Reinhardt, Blanchard, and Harper have developed techniques that allow industry to apply a no-wrinkle finish to cotton fabric - both broadcloth and knits - before dyeing. Based at ARS' Textile Finishing Chemistry Research Unit in New Orleans, they have added to the no-wrinkle finish solution a variety of quaternary ammonia salts, also found in products such as chicken feed and fabric softeners. By adding a positive charge to the fabric, the modified finish attracts dyes, allowing no-wrinkle cotton to be dyed.

The New Orleans scientists are also looking at derivatives of triethanolamine - a chemical found in some hand lotions and shampoos - to add to the no-wrinkle finish formula.

The new techniques should increase cotton's marketability against synthetic fibers. Several patents have been issued on this technology, and other patent applications have been filed. Some of these techniques are currently being evaluated by the textile industry.

The modified finishes do more than enable industry to broaden use of no-wrinkle finishes without losing money to a fashion color change. They also broaden the choice of dyes that can be used, giving the industry more options for supplies as well as a wider range of shades and deeper, more vibrant colors.

Only certain classes of dyes - direct, reactive, and vat - can be used on untreated cotton fabric, Reinhardt says. However, the additives in the modified finishes have a positive charge, which attracts the acid dyes now used to color wool and nylon. Shades that can't be gotten with standard cotton dyes may be possible with acid dyes. What's more, he adds, in some cases the modified finishing process improves uptake of standard dyes, resulting in deeper hues.

Blanchard says washing tests have shown that fabric dyed by the modified process retains color as well as non-finished fabric. In some tests, it was even more color-fast.

For those popular stone-washed and ice-washed jeans, the group's research can make it more cost-effective to produce a no-wrinkle garment. To achieve the irregular stone-washed look, industry now puts dyed garments in a tumbler with porous volcanic rocks called pumice stones. The stones wear down the fabric, creating an irregular pattern. In ice-washing, the garments are tumbled with stones that have been soaked in bleach to create a similar irregular pattern.

"This all might sound a bit wild," says Harper, "but then, who would have thought that stone-washed jeans would have become so popular?"

Harper and co-workers have also used the modified finish to create a "mock denim" that gives the industry a shortcut in making denimlike fabric. To make real denim, dyed yarns are cross-woven with white yarns.

The new technique shortens his process into one dyeing step. This is done by placing large screens, normally used to print designs on fabric, on top of undyed fabric. When the modified no-wrinkle finish is applied through the screen, it contacts only the raised yarns. After the fabric has been heated, the treated yarns - those that run leghtwise - hold a positive charge and will accept dyes. Yarns that run crosswise don't have a charge and will not accept dyes. Finally, the fabric is dyed to create the denim effect.

Harper says, "this technique gives industry more versatility in jeans' color." Rather than committing to thousands of yards of blue yarn, for instance, textile manufacturers can used undyed yarn and produce a generic treated fabric that can be dyed any color they want.

Another finishing approach for unique design in a large-scale dyeing operation. This is done by modifying a textile finishing machine with lace to give an uneven application of the finishing formulation to fabric. Then, when the fabric is dyed in a dye bath, only the positively charged areas take the color, resulting in the design. The researchers have also devised ways of achieving multicolored fabric. These are based on either changing dye-bath pH in order to dye treated areas of the fabric with one color and untreated areas with another color or by using different agents that either remain on the fabric surface or penetrate deep into the cotton and respond to different classes of dyes.

And to achieve the effect of hand-dyed, tie-dye shirts, Harper and co-workers have found a way for the garment industry to do it for the consumer. They call this technique "rope finishing." Fabric is twisted in a ropelike fashion and subjected to a modified finish.

After the fabric is finished, it is untwisted, spread flat for drying and curing, then dyed. Only the finished areas of the fabric will accept dyes.

These new dyeing techniques allow the clothing industry to be more responsive to consumer demand. - By Bruce Kinzel, ARS.

PHOTO : Colorful, dyeable smooth dried cationic cotton fabrics are examined by chemist Robert Harper, Jr. (K-3837-13)
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Title Annotation:techniques that dye cotton after treatment with a no-wrinkle finish
Author:Kinzel, Bruce
Publication:Agricultural Research
Date:Feb 1, 1991
Words:1052
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